A flight attendant (FA) sustained a serious injury on Southwest Airlines flight 5797 when it encountered turbulence during cruise flight while enroute to Charleston International Airport (CHS), Charleston, South Carolina. Southwest Airlines reported that their flight attendant jumpseat positions are as follows on the 737-800 aircraft: the “A” and “C” FA’s are positioned in the forward galley and the “B” and “D” FA’s are positioned in the aft galley. The flight crew reported that before the flight, the captain briefed the two forward galley position FAs to expect a “rough” ride after departure on the initial climb and that if smooth air was encountered it would not last long. He also informed them of a line of convective weather that they would need to deviate through, and that they should expect turbulence until they were well clear of that weather. Although the captain was not able to meet with the two aft galley FAs before departure, he was assured that the preflight briefing would be relayed to them. The flight crew reported that the climb and initial cruise flight was turbulent; however, they briefly experienced a smooth ride for about 20 minutes before the flight was expected to encounter another area of turbulence. The captain stated that he had notified the FA’s that if they got up, he wanted them in their seats at least five minutes before the expected turbulence and provided a specific time for them to be seated. After the brief smooth ride, the flight experienced the expected continuous light to moderate turbulence as the flight crew navigated through a line of convective weather. The turbulence persisted longer than initially anticipated, so the captain called the FA’s to advise them to expect continued turbulence. At this time, the captain was informed that the “D” position FA had injured herself by splashing a pot of coffee onto her head, face, and shoulders. The “B” position FA reported that the captain had notified the FA’s that the flight might encounter turbulence and to remain seated if the rough air materialized. Due to the smooth air encountered during the initial cruise portion of the flight, the FA’s were able to quickly complete a passenger service and be reseated. The “B” position FA recalled that the captain had asked the FA’s to take their seats before the second area of turbulence was encountered. The “D” position FA reported that she brewed a fresh pot of hot coffee for the passengers. After brewing the coffee, she picked up the coffee pot by its handle to pour a cup. However, at that moment, the aircraft encountered turbulence, causing the coffee pot to strike a handle near the coffee machine. As a result, hot coffee splashed on her. Upon being notified of the injury, the captain messaged dispatch via the aircraft communications addressing and reporting system and coordinated to have medical personnel meet the airplane upon arrival at the gate. The aircraft was met by paramedics who immediately transported the injured FA to a hospital where she was diagnosed with second degree burns.